Liquid crystal displays transmitting light in a transparent state and blocking light in a non-transparent state are generally known. Due to the orientation times of molecules of the liquid crystals used in such a liquid crystal display and to triggering effects with transient and dying-down voltage curves, a transparent state is usually to be understood as a nearly transparent state and a non-transparent state or opaque state is to be understood as a nearly opaque state.
Usually, liquid crystal displays are made up of several layers including two support layers made of glass or plastic, which have one electrode layer, respectively, on each of the surfaces facing each other. Here, one of the electrode layers is subdivided into a multiplicity of individual electrodes in order to assign pixels to each of the respective surfaces of the electrode. The electrodes are formed from indium-tin-oxide (ITO) which is a nearly transparent, but conductive material. Spacers are disposed between the two electrode layers, in order to keep a distance between the electrode layers. In the space between the electrode layers, the liquid crystals are provided, which will orient themselves in accordance with a voltage applied between the two electrodes.
Polarizers in the form of films are applied on the outside of the two support materials. If no voltage or a voltage particularly well below a threshold value is applied to the electrodes, the molecules of the liquid crystals will be oriented such that light may pass through the entire assembly. If the voltage applied to the electrodes exceeds the threshold value, the molecules will re-orientate themselves so that the light incident in the crystal layer is turned and light will be prevented from passing.
FIG. 7 shows an example of an assembly of electrodes 1, 2 as well as a voltage characteristic for triggering the electrodes in such a liquid crystal display. A first electrode layer is subdivided into a multiplicity of individual electrodes 1 used to trigger individual pixels. The second electrode layer is formed as a continuous electrode 2. A voltage V is applied to the individual electrodes, which reaches or exceeds a threshold value VD for switching into a non-transparent state. For triggering a transparent state, the voltage V applied between the electrodes 1, 2 will be left below the threshold value VD.
In the first state with an applied voltage V above the threshold value VD, instead of a constant voltage V with a constant value, an alternating voltage V will be applied in such a way that the voltage will alternately exceed and fall below a positive and a negative threshold value VD, VD−, in order to avoid a burn-in effect. The voltage V is therefore usually to be understood as a voltage differential which will be applied between the electrodes effectively nominally and independent from a zero point.
Moreover, touch-sensitive input devices are generally known, which are also formed on the basis of designs having principally the same structure as a liquid crystal display. Such touch-sensitive devices on the basis of ITO electrodes, which are arranged in a spaced relationship to each other, are structurally different from liquid crystal displays particularly due to the fact that no liquid crystal layer is provided in the space between the electrodes. The capacitive sensor layers almost exclusively only include one layer made of metallically transparent electrodes.
At least one of the ITO layers for forming an electrode layer is formed with a multiplicity of individual electrodes and is applied onto an elastic material such as, for example, a film. By applying pressure onto the elastic material, the electrode layers, which are normally spaced apart from each other by the spacer layer, will come into contact with each other, so that a current flow over individual ones of the electrodes is created. An evaluation circuit can assign the current flow of individual electrodes to a certain position on the touch-sensitive input device.
In accordance with another embodiment, the individual electrodes are connected to the evaluation circuit via the capacitor circuit outlined in FIG. 8, in order to detect a capacity change instead of a current flow. In the case of such an arrangement, a saw tooth-shaped sensor voltage VS is applied in a certain timing sequence over a multiplicity of clocks clk to the electrodes lying opposite each other. Once a sensor threshold voltage VSS is reached, the sensor voltage VS will be reset to the initial value and the number of clocks clk elapsed since the last initial value will be counted. Once a certain number of clocks clkT is exceeded, this will be used as a criterion for an object approaching the touch-sensitive device in the area of the corresponding electrodes. The approach of a capacitively active object towards the corresponding electrodes causes a change in the capacity value which will result in a correspondingly longer period of time for the sensor threshold voltage VSS to be reached and thus in a larger number of clocks clkT.